The Origins of O

A strain of HIV that has afflicted more than 100,000 people emerged from gorillas.

May 1, 2015

Kerry Grens

TRANSMITTER: Western lowland gorillas appear to be the source of a particular type of HIV that has infected 100,000 humans. PIXABAY.COM

EDITOR'S CHOICE IN MICROBIOLOGY

The paper
M. D’arc et al., “Origin of the HIV-1 group O epidemic in western lowland gorillas,” PNAS, doi:10.1073/pnas.1502022112, 2015.

The strains
HIV jumped from apes to humans at least four times, as evidenced by genetically distinct groups of the virus that have been detected: M, N, O, and P. While N and P have had little impact, M is responsible for the pandemic affecting millions of individuals, and O has infected another 100,000.

The origin
The M group of HIV-1 came from chimpanzees, likely in Cameroon. To uncover the roots of group O, Martine Peeters at INSERM and the University of Montpellier in France and colleagues trekked into the forests of central Africa to collect and analyze fecal samples from chimps and, while they were at it, from gorillas, too. “It became clear the O group is most closely related to the gorilla virus,” says Peeters’s collaborator Beatrice Hahn of the University of Pennsylvania.

The chink in the armor
Phylogenetic comparisons of various simian immunodeficiency viruses (SIVs) point to a gorilla having caught the virus from chimps. To understand how, the researchers scrutinized an antiviral protein, APOBEC3G, in gorillas. They found that it was vulnerable to counteractivity by a gorilla SIV protein, Vif, but not to Vif from chimp SIV. “The Vif protein must have changed, because it can overcome” APOBEC3G, says Welkin Johnson, a virologist at Boston College. “It’s a direct example of how this APOBEC3G protein must be a genetic barrier to viruses jumping between species.”

The consequences
Peeters points out that people infected with group O virus can be resistant to one type of HIV medication. Understanding the genetic diversity of HIV, she says, “has implications for diagnosis, treatment, and also vaccine development.”